1. Field of the Invention
This invention relates to the preparation of graft copolymers and more particularly to the preparation of graft copolymer of ABS (acrylonitrile-butadiene-styrene) type by a modified suspension process.
2. Description of the Prior Art
ABS resin technology has grown from its original concept which involved blending of styrene-acrylonitrile resin with nitrile rubber to new areas of technology involving graft polymerization wherein the monomers, styrene and acrylonitrile, are copolymerized onto rubber substrates or backbones and such copolymerizations have been accomplished in mass, emulsion, solution or suspension. As reported in the section on ABS Technology in the "Modern Plastics Encyclopedia", 1968, the rubber elastomeric phase can comprise a variety of elastomers and the relationships of the various components which include styrene and acrylonitrile can be controlled to take maximum advantage of a single property or a set of properties.
In today's market there appear ABS interpolymers of various melt flows and impact strengths which can be used to form glossy sheet, extruded pipe and a variety of molded articles requiring the good properties of ABS resins. The present ABS products on the market finding the widest acceptance and commercial demand are those based on latex technology; that is, that technology wherein emulsion polymerization recipes are employed in forming not only the elastomeric component, commonly polybutadienes, but also the final ABS product, thereby requiring various steps in the process and equipment and making these resins somewhat more complex and expensive to prepare than the simple blends of the early ABS art. These modern day ABS products accordingly sell for a premium in view of the complex technology and cost in their manufacture. It is apparent that industry desired processes and/or techniques for manufacture of ABS resins which can reduce either the cost and/or complexity of manufacture while at the same time provide resins which are equivalent in properties and performance.